Aerospace gas turbine engines require compact combustors that exhibit good flame stability and high combustion efficiency. For a typical aerospace engine, the combustor compactness is substantially dictated by the volume required for liquid atomization, mixing with combustion air, and combustion of the resulting mixture. This resulting mixture often consists of droplets in a heterogeneous fuel/air mixture. Consequently, heterogeneous burning of the resulting mixture usually requires extended combustion times due to need of residence time to fully vaporize the droplets prior to combustion. However, such extended combustion times often lead to larger combustion zones, lack of flame stability and high pollutant emissions, particularly of unburned hydrocarbons.
Existing engine concepts reduce time-to-combust by enhancing mixing/evaporation rates through devices such as turbulence generators or flow swirlers. These devices lead to an increased combustor pressure drop and may lead to flame instability, particularly in part-load situations. For a high performance aerospace combustor, typical times from injection to final fuel burn-out (“residence time”) of the combustion process can be roughly specified as follows: 1 to 3 ms for the fuel spray to distribute through the air followed by 2 to 3 ms for droplet vaporization with combustion taking an additional 1 to 2 ms. This leads to a total required residence time of 4 to 8 ms which may be too long for certain combustor designs, in particular, interturbine combustors.
Alternately, as seen in Trapped Vortex Combustors (TVC), a region of the combustor can be designed such as to locally produce a residence time sufficiently long to achieve combustion, and the heat/intermediate products from this region anchor the flame in the fast moving regions of the combustor.
None of the prior art, however, provides a compact combustor that exhibits good flame stability and high combustion efficiency in an aerospace gas turbine engines require. Therefore, it is an object of the present invention to provide a viable improved combustor for aircraft engines that exhibit good flame stability and high combustion efficiency.